By shifting some of the Mississippi's flow from its southernmost branch, the Atchafalaya River, to the Mississippi's main river body could create a strong current of fresh water that would act as a barrier against the oil. (Read how nature is fighting the Gulf oil spill.)

At the fork, a human-made water-flow management system diverts 70 percent of the water to the lower Mississippi and 30 percent to the Atchafalaya. (Test your Mississippi River knowledge.)

This is done to prevent the river's course from changing over time, as it naturally would, and encroaching into cities such as New Orleans. The river eventually empties into the Mississippi River Delta, located on Louisiana's Gulf Coast (see map.) The Atchafalaya empties farther west into the Gulf, in a region not yet threatened by the oil.

But Kemp proposes changing the ratio to 80-20 for the next few weeks, allowing the Mississippi to flow more robustly and cleanup crews more time to deal with the crisis.

"A lot of people are coming up with ideas about what to do about the oil spill, and the river is actually our best tool," he said.

The Mississippi will not be able to keep the oil at bay indefinitely, however. The river's flow naturally declines each summer, and by August, Kemp's idea will no longer be effective.

That's why Kemp rushed to submit a memo on June 9 outlining his idea to the U.S. Environmental Protection Agency, which would have to approve any short-term river diversions.

Open Dams to Fight Oil Spill?

In addition to rerouting the Mississippi, Kemp suggests that water currently held behind dams farther upriver should be slowly released. This would keep the flow of water as strong as possible.

"These are two things that are probably the most important things you can do to keep oil out of the marshes and Louisiana," Kemp said.